SELENIUM, in Chemistry, a new substance recently discovered by Professor Berzelius, and ranked by him among the metals; though some chemists are doubtful whether it might not, with greater propriety, be classed with sulphur, and phosphorus. This substance was obtained by Berzelius from the pyrites of Fablun, in Sweden. Its colour is gray ; it has a brilliant metallic lustre, and is slightly transparent. It softens when heated, to 212° Fehr., and melts at a few degrees higher. When cooling it may be drawn into fine threads, having likewise a strong metallic lustre ; when cooled slowly, it breaks with a granular fracture. At 600° it boils; and that portion which is volatilized, on becoming cool, either condenses into opaque metallic drops, or else is sublimed in the form of a. fine red powder.. When submitted to the blow-pipe, it tinges the flame of a beautiful azure, and emits a strong smell of horse-radish. It conducts
heat very sparingly, and electricity not at all. Selenium, when heated in nitric acid, is dissolved, and a part of the acid combining with the oxygen of the mineral, forms selenic acid; which acid being first evaporated to dryness, may, by the application of heat, be either volatilized, or made to form crystals in needles, some of which are found to be a foot in length. These crystals are soluble in water. Selenic acid united readily with the fixed alkalies, forming with them the salts called selenites, which have the colour of vermilion, crystal lize with difficulty, and deliquesce on exposure to the action of the atmosphere. By introducing a plate of zinc into an aqueous solution of any of these salts, the selenium will be precipitated in a metallic state. See Ure's Dictionary of Chemistry.